Studies of routes of energy losses from neoplastic cells continued using a model consisting of a control rat hepatocyte line and its N-nitroso-N-methlyurea-transformed counterpart. Studies of energy loss focused on the enzyme, lactic dehydrogenase (LDH, E.C. 1.1.1.27), because it is known to produce lactic acid in larger quantities in neoplastic cells and to export it into the medium, representing an energy loss. Five subtypes of LDH were identified with isoelectric points between pH 5.98 and 9.44 in control cells but only two in tumorigenic cells. The latter correlate with markedly increased rate of synthesis and excretion of lactic acid. The availability of new monoclonal antibodies against tubulin, cytokeratin and actin resulted in more clearly defined differences between the control and tumorigenic rat hepatocyte lines. In the latter, cytokeratin in markedly diminished in fluorescence, but the aggregation pattern is not altered; tubulin and actin are altered in the patterns of their individual aggregates and also show a slight overall decrease in fluorescence.